1. Field of the Invention
This invention relates to monolayer sugar-coated tablet which is coated with single sugar-coating liquid of specific composition and process for preparation thereof. Because the monolayer sugar-coated tablet of the invention is prepared in single step using a single sugar-coating liquid, it does not require the skill and high technical level of artisans which are normally demanded for ordinary sugar-coating processing. Furthermore, it allows reduction in consumption of sugar-coating material and reduction in processing time, and is economically very advantageous.
2. Description of the Prior Art
Sugar-coating has been widely practiced with pharmaceutical formulations not only for imparting regular shapes to sugar-coated tablets to improve the latter's appearance, but also for the purpose of increasing moisture-proof property to prevent deterioration of the coated product and facilitate administration. Whereas, conventional sugar-coating method requires plural steps including sub-coating, smoothing, coloring, finishing and polishing, and hence need many processing hours. Furthermore, skills are essential for the operations and because the composition of sugar-coating liquid used is normally different for each step, formulation and preservation of those liquids cost much labor. Comparing with methods for preparing other formulations, therefore, the method is considerably cost-taking.
Namely, in generally practiced preparation method of a sugar-coated tablet, first in the sub-coating step uncoated tablets are coated with a sugar-coating liquid whose chief components are saccharide, additives and binder, several tens of times to round the angular portions of the uncoated tablets; then coated with a sugar-coating liquid containing less amount of the additives and having an increased concentration of saccharide several times in the smoothing step, to smooth out the sub-coated layer surface. If necessary the tablets are then sent to a coloring step, wherein they are coated with a pigment-containing sugar-coating liquid several times to be colored, followed by a finishing step in which the surfaces of the tablets are given smoothness suitable for polishing. Finally wax or the like is scattered on the tablets in a polishing step to impart gloss to their surfaces and provide the finished sugar-coated tablet.
Preparation of sugar-coated tablet thus generally requiring complex, multi-step processing and considerably long processing time, attempts to simplify the sugar-coating steps and shorten the processing time have been reported in the past. For example, Laid-open (Kokai) Patent Application Sho 51(1976)-70808A-JP disclosed a sugar-coating method in which sub-coating and/or smoothing steps are dispensed with, by using a sugar-coating liquid obtained by addition of an inorganic high molecular weight substance chiefly of montmorillonite to aqueous solution of sucrose. Kokai Sho 56(1981)-87518A-JP disclosed a preparation process of thin-layer sugar-coated tablets which were spray-coated with about 9 to 40% to the weight of uncoated tablets of a sugar-coating liquid containing about 10–80% by weight of talc to the sugar as suspended in said liquid. Sho 56(1981)-39287B1-JP disclosed a process for making sugar film-coated tablets in which the uncoated tablets were directly coated with a film of a sugar-coating liquid containing at least 10% by weight of polyvinyl alcohol, not more than about 35% by weight of saccharide and an adequate amount of a tackiness-reducing agent. The sugar coatings obtained in those methods, however, are invariably thin, and the sugar-coated tablets obtained thereby cannot fully exhibit the properties characteristic of sugar-coated tablet. Kokai Hei 9(1997)-175997A-JP, furthermore, disclosed a method of coating with a sugar-coating liquid containing 1–4 parts by weight of hydroxypropylmethylcellulose having specific properties and 5–25 parts by weight of a filler formed chiefly of finely pulverized talc. Said process, however, allowed to carry out the sub-coating step and smoothing step using a sugar-coating liquid of identical composition, but the subsequent finishing step and polishing step could not be omitted. Hei 7(1995)-17497B1-JP disclosed a sugar-coating method comprising sprinkling a sugar-coating liquid which contained 40–65% by weight of saccharide and 0.04–1.6% by weight of a surfactant. However, because the sugar-coating liquid used in this method contained the surfactant at such a low ratio, the resulting sugar-coated tablet lacked sufficient smoothness and its gloss also was unsatisfactory.